1. Field of the Invention
This invention relates to a semiconductor laser device.
2. Background Art
In semiconductor laser devices, a high optical output is achieved by increasing the level at which COD (catastrophic optical damage) occurs. To increase the COD level, AlGaAs-based and InGaAlP-based semiconductor laser devices are often based on a window structure in which the active layer near the end faces to constitute an optical resonator is disordered to widen the bandgap and reduce optical absorption.
However, in InGaN-based blue-violet semiconductor laser devices for the next-generation DVD (digital versatile disc), the active layer is difficult to disorder, and the window structure is difficult to use. In a structure to solve this difficulty, for example, a current non-injection region, where no electrode is formed, is provided near the end face to prevent temperature increase due to non-radiative recombination and increase the COD level.
In this case, the vicinity of the boundary between the electrode non-formation region without current injection and the electrode formation region undergoes a stress-induced strain due to temperature increase and decrease of several hundred ° C. in the laser element mounting process. Such a stress-induced strain deteriorates the characteristics and reliability of the laser element.
JP-A 2004-186708 (Kokai) discloses a technique related to a gallium nitride-based semiconductor laser element having good lasing characteristics as a light source for optical disks. This technique provides a gallium nitride-based semiconductor laser element in which the length, along the laser resonator, of the ohmic electrode for supplying a current to the active layer is shorter than the length of the laser resonator. However, this structure is insufficient for preventing the stress-induced strain.